JP2016076421A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve soundness of a spark plug by improving push-back resistance of a center electrode.SOLUTION: A spark plug includes an insulator, a center electrode, a terminal fitting and a main fitting. The center electrode includes: a front end side electrode part including a portion protruding from a front end of a shaft hole of the insulator; a flange part which is provided at a rear end side of the front end side electrode part and of which the outer diameter is larger than that of the front end side electrode part; and a rear end side electrode part which is provided at a rear end side of the flange part and of which the outer diameter is smaller than that of the flange part. A gap between the rear end side electrode part and an inner peripheral surface of the insulator is filled with a first filler powder. Further, ruggedness is formed in at least a part of a portion in contact with the first filler powder that fills the gap, on the inner peripheral surface of the insulator.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a spark plug.

  A spark plug used for an internal combustion engine generally includes a cylindrical metal shell, a cylindrical insulator disposed in an inner hole of the metal shell, and a center disposed on a tip side of a shaft hole of the insulator. And an electrode, a terminal fitting disposed on the rear end side of the shaft hole, and a ground electrode having one end joined to the distal end side of the metal shell and the other end facing the center electrode to form a spark discharge gap.

  As a kind of spark plug, there is a type of spark plug in which a filler powder such as talc is filled around the rear end portion of the center electrode in order to make the center electrode fixed to the insulator more reliably (see FIG. Patent Documents 1 and 2).

JP 2011-1113836 A JP-A-57-101365

  However, the inventor of the present application has found that the soundness of the spark plug may be impaired if the fixing power of the filling powder is reduced by heating or vibration of the engine. That is, when the tip of the center electrode is pressurized by the pressure of the combustion gas in a state where the adhering power of the filling powder is reduced, the center electrode is pushed back (the center electrode is pushed to the rear end side and the shaft hole of the insulator is May deviate from the normal position). When pushback of the center electrode occurs, there is a problem that the soundness of the spark plug is impaired (specifically, a spark discharge gap is increased and ignition failure occurs).

  In recent years, since the thickness of each member has been reduced with the miniaturization of the spark plug 100, the soundness of the spark plug is easily impaired when various ideas are added to the shape of each member. There is a problem.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, an insulator having an axial hole extending in the direction of the axis, a center electrode protruding from the tip of the axial hole, a terminal fitting protruding from the rear end of the axial hole, A metal shell for housing the insulator, wherein the center electrode is provided on a distal end side electrode portion including a portion protruding from a distal end of the shaft hole of the insulator, and on a rear end side of the distal end side electrode portion. A rear end electrode portion having a flange portion having an outer diameter larger than that of the distal end side electrode portion, and a rear end side electrode portion provided on the rear end side of the flange portion and having an outer diameter smaller than that of the flange portion. And a spark plug filled with a first filling powder between the inner peripheral surface of the insulator. The spark plug is characterized in that an uneven portion is formed in at least a part of a portion of the inner peripheral surface of the insulator that is in contact with the filled first filled powder.
According to the spark plug, the unevenness on the inner peripheral surface of the insulator increases the adhesion force between the insulator and the first filling powder, so that the pushback resistance of the center electrode can be improved, and the spark can be increased. It is possible to improve the soundness of the plug.

(2) In the spark plug, when the diameter of the shaft hole at the tip of the insulator is φd, and the length of the portion in contact with the first filling powder in the concavo-convex portion is L1. L1 / φd ² ≧ 0.3 mm ⁻¹ may be satisfied.
According to this spark plug, it is possible to further improve the push plug resistance of the center electrode and further improve the soundness of the spark plug.

(3) In the spark plug, the inner peripheral surface of the insulator has a stepped portion with which the inner diameter increases toward the rear end side and the flange portion of the center electrode contacts at least a part of the inner surface. Then, in the axial direction, when the length from the rear end of the insulator to the stepped portion is L0 and the length of the uneven portion is L3, L3 / L0 ≦ 0.6 may be satisfied. .
According to this spark plug, since the length L3 of the concavo-convex portion does not become excessively large, the concavo-convex portion on the inner peripheral surface of the insulator becomes excessively long, and the rear end portion of the insulator is bent during manufacture of the insulator. This can prevent the loss of soundness of the spark plug.

(4) In the spark plug, the uneven portion is formed by a thread groove continuous with a female screw portion provided at a rear end of the shaft hole so as to be screwed with a male screw portion of the terminal fitting. It is good.
According to this spark plug, it is possible to easily provide an uneven portion to be fitted with the powder filling portion.

(5) In the spark plug, a second filling powder is filled between the tip side electrode portion and the tip side inner peripheral surface of the insulator, and a second filling powder is provided on the outer peripheral surface of the tip side electrode portion. It is good also as what is provided with the uneven | corrugated | grooved part.
According to this spark plug, the second concavo-convex portion provided on the outer peripheral surface of the tip electrode portion of the center electrode increases the fixing force between the center electrode and the second filling powder. Pushback resistance can be further improved, and the soundness of the spark plug can be improved.

(6) In the spark plug, the length of the second concavo-convex portion in the axial direction may be 10 mm or more.
According to this spark plug, the adhesion force between the center electrode and the second filling powder is further increased, so that the pushback resistance of the center electrode can be further improved, and the soundness of the spark plug is improved. Is possible.

  Note that the present invention can be realized in various modes. For example, it is realizable with forms, such as a manufacturing method of a spark plug.

The front view which shows the spark plug as one Embodiment. Sectional drawing of an insulator, a center electrode, and a terminal metal fitting. Explanatory view showing the effect of by the parameter L1 / .phi.d ² to push back strength. Explanatory drawing which shows the influence on the pushback intensity | strength by the length A of the uneven | corrugated processed part of a center electrode. Explanatory drawing which shows the influence on the bending of the insulator by parameter L3 / L0.

  FIG. 1 is a front view showing a spark plug 100 as an embodiment of the present invention. In FIG. 1, the lower side where the ignition part of the spark plug 100 exists is defined as the front end side of the spark plug 100, and the upper side is defined as the rear end side. The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50. The insulator 10 has an axial hole extending along the axis O. The axis O is also referred to as “center axis”. The center electrode 20 is a rod-shaped electrode extending along the axis O, and is held in a state of being inserted into the shaft hole of the insulator 10. The ground electrode 30 is an electrode having one end fixed to the tip 52 of the metal shell 50 and the other end facing the center electrode 20. A spark discharge gap is formed between the tip of the center electrode 20 and the ground electrode 30. The terminal fitting 40 is a terminal for receiving power supply, and is electrically connected to the center electrode 20. The metal shell 50 is a cylindrical member that covers the periphery of the insulator 10, and fixes the insulator 10 inside. A screw portion 54 is formed on the outer periphery of the metal shell 50. The screw part 54 is a part where a screw thread is formed, and is screwed into a screw hole of the engine head when the spark plug 100 is attached to the engine head.

  FIG. 2 shows a cross section of the insulator 10, the center electrode 20, and the terminal fitting 40. The shaft hole 11 of the insulator 10 has a small diameter portion 11r1 on the front end side, a large diameter portion 11r2 on the rear end side, and a step portion 11stp between them. The step portion 11stp is a portion whose inner diameter increases toward the rear end side.

  The large diameter portion 11r2 is a portion extending from the step portion 11stp to the rear end of the insulator 10 and has a length L0. The length L0 corresponds to the length from the rear end of the insulator 10 to the step portion 11stp in the axial direction. In the large diameter portion 11r2, a concavo-convex portion 11ue is formed from the rear end of the insulator 10 to the length L3. As shown in the enlarged view on the left side of FIG. 2, the uneven height of the uneven portion 11 ue is t. The concavo-convex portion 11ue is formed as a screw groove continuous to the female screw portion provided at the rear end of the shaft hole 11 so as to be screwed with the male screw portion of the terminal fitting 40. That is, the terminal fitting 40 is screwed into the rear end portion of the uneven portion 11ue. The length L3 of the concavo-convex portion 11ue in the shaft hole 11 is assumed to be a virtual cylindrical surface that coincides with the inner surface of the large-diameter portion 11r2 where there is no concavo-convex portion 11ue, and is projected or recessed from the cylindrical surface. It is measured as the length of the range between the upper and lower ends of the part.

  The center electrode 20 is provided on the rear end side of the distal end side electrode portion 22 including the portion protruding from the distal end of the shaft hole 1 of the insulator 10 and has a larger outer diameter than the distal end side electrode portion 22. It has a collar part 24 and a rear end side electrode part 26 which is provided on the rear end side of the collar part 24 and has an outer diameter smaller than that of the collar part 24. The flange portion 24 is disposed on the rear end side of the step portion 11stp of the shaft hole 11 of the insulator 10, and is in contact with at least a part of the step portion 11stp. The rear end of the rear end side electrode portion 26 is inserted into a bottomed hole formed at the front end portion of the terminal fitting 40. The distal end 22 e of the distal end side electrode portion 22 protrudes from the distal end portion 10 e of the insulator 10. The shaft hole 11 at the distal end portion 10e of the insulator 10 has a diameter φd. In the example of FIG. 2, an uneven surface 22 a processed by uneven surface processing such as knurling or honing is formed over the length A on the outer peripheral surface of the distal electrode portion 22. However, the concave and convex portion 22a can be omitted. In addition, the uneven | corrugated processed part 22a is also called a "2nd uneven | corrugated part."

  In the large diameter portion 11r2 of the shaft hole 11 of the insulator 10, a powder filling portion 60 filled with the first filling powder 62 is formed over the length L2. The first filling powder 62 is a powder for fixing the first filling powder 62 by filling the space between the rear end side electrode portion 26 of the center electrode 20 and the inner peripheral surface of the insulator 10, for example, talc. Etc. are formed. The length of the portion where the powder filling portion 60 and the uneven portion 11ue on the inner surface of the shaft hole overlap (referred to as “fitting length”) is L1. That is, the fitting length L1 is a length in the axial direction of a portion of the concavo-convex portion 11ue that is in contact with the first filling powder 62.

  The small diameter portion 11r1 of the shaft hole 11 of the insulator 10 is filled with the second filling powder 72. The second filling powder 72 is a powder for fixing both the end electrode portion 22 of the center electrode 20 and the tip end inner peripheral surface of the insulator 10 by filling them. As this 2nd filling powder 72, the powder of various inorganic adhesive agents, such as a mixture of ceramic powder and water glass, or cement, can be utilized, for example.

Examples of the various dimensions in FIG. 2 and their typical values are as follows.
(A) L0: Length of the large diameter portion 11r2 of the shaft hole 11 of the insulator 10 (15 to 60 mm)
(B) L1: The fitting length of the powder filling part 60 and the uneven part 11ue (0 to 10 mm)
(C) L2: Length of the powder filling unit 60 (10 to 30 mm)
(D) L3: Length of the uneven portion 11ue on the inner surface of the shaft hole of the insulator 10 (5 to 30 mm)
(E) A: Length of the uneven portion 22a on the outer surface of the tip electrode portion 22 of the center electrode 20 (0 to 30 mm)
(F) φd: Diameter of the shaft hole 11 at the tip 10e of the insulator 10 (1 to 4 mm)
(G) t: Concave and convex height of the concave and convex portion 11ue (0.1 to 1.0 mm)

  Note that the uneven portion 11 ue to be fitted with the powder filling portion 60 does not need to be continuous with the female screw portion provided at the rear end of the shaft hole 11 and is separated from the female screw portion provided at the rear end of the shaft hole 11. It may be. However, it is preferable that the concavo-convex portion 11 ue be formed easily if the concavo-convex portion 11 ue is formed as a screw groove continuous with the female screw portion provided at the rear end of the shaft hole 11.

Figure 3 is an explanatory diagram showing the effect of the push-back strength according to the parameter L1 / .phi.d ² for a plurality of samples having the shape of FIG. The first six samples S10 to S15 are obtained by changing the fitting length L1 of the powder filling portion 60 and the uneven portion 11ue by changing the length L3 of the uneven portion 11ue, and other dimensions are the samples S10 to S15. All are the same. The next samples S20 to S25 also have different fitting lengths L1 between the powder filling portion 60 and the concavo-convex portion 11ue by changing the length L3 of the concavo-convex portion 11ue, and all other dimensions are the samples S20 to S25. The same. However, in the samples S10 to S15, the diameter (tip hole diameter) φd of the shaft hole 11 at the tip portion 10e of the insulator 10 is 3.0 mm, whereas in the samples S20 to S25, the tip hole diameter φd is 2.0 mm. Both are different.

The second column from the right end of FIG. 3, there is described a value of the parameter L1 / .phi.d ² of each sample, the rightmost column are described pushback strength test determination result. The determination result of the pushback strength was obtained based on the maximum load when the end surface of the tip 22e of the center electrode 20 of the sample having the shape shown in FIG. 2 was pushed in the direction of the axis O using a compression tester. Is. The pushback strength is also referred to as “pushback resistance”. According to the results of FIG. 3, it can be understood that preferred because the value of the parameter L1 / .phi.d ² becomes higher pushback strength enough to increase.

Why the parameter L1 / .phi.d ² affects the pushback strength is as follows. That is, the longer the fitting length L1 between the powder filling portion 60 and the uneven portion 11ue, the stronger the fixing force between the first filling powder 62 and the uneven portion 11ue in the shaft hole 11. Therefore, the pushback strength tends to increase as the mating length L1 increases. On the other hand, since the square φd ² of the tip hole diameter φd of the insulator 10 is substantially proportional to the cross-sectional area of the center electrode 20, the load on the center electrode 20 increases in proportion to φd ² . Therefore, the pushback strength tends to decrease as φd ² increases. Considering these points, pushback strength, it is possible to estimate that there is a tendency to increase in accordance with the parameter L1 / φd ^2. The result of FIG. 3 also shows this tendency.

According to the results of FIG. 3, if the parameter L1 / .phi.d ² is 0 (i.e., if the powder filling portion 60 and the concave-convex portion 11ue is not fitted) in comparison with, if it exceeds the parameters L1 / .phi.d ² is 0 ( The case where the powder filling portion 60 and the concavo-convex portion 11ue are engaged is preferable in that the pushback strength is high. The value of the parameter L1 / .phi.d ² is preferably set to 0.3 mm ^-1 or more, more preferably to 0.4 mm ^-1 or higher, and most preferably 0.5 mm ^-1 or higher.

  FIG. 4 is an explanatory diagram showing the influence on the pushback strength due to the length A of the concavo-convex portion 22 a of the center electrode 20. These five samples S31 to S35 are obtained by changing only the length A of the concavo-convex portion 22a, and other dimensions are the same as those of the samples S31 to S35. The sample S31 is the same as the sample S12 in FIG. According to the result of FIG. 4, it is preferable in that the pushback strength increases as the value of the length A of the concavo-convex portion 22a increases. The reason for this is that the second filling powder 72 is filled around the distal electrode portion 22 having the concavo-convex portion 22a, so that the longer the concavo-convex portion 22a is, the longer the second filling powder 72 and the concavo-convex portion are. This is because the adhering force between 22a increases. The length A of the concavo-convex portion 22a may be 0 mm, but is preferably 5 mm or more, and more preferably 10 mm or more.

  3 and 4, the length L2 of the powder filling portion 60 is 20 mm. However, it is considered that the pushback strength increases as the length L2 of the powder filling portion 60 increases. Considering this point, it is preferable to set the length L2 of the powder filling portion 60 to a sufficient length (for example, 15 mm or more).

  FIG. 5 is an explanatory diagram showing the influence of the parameter L3 / L0 on the bending of the insulator 10. The insulator 10 in the present embodiment is obtained by firing a molded body obtained by molding a material powder by a known molding method using a known firing method. Here, the bending of the insulator 10 means that the molded body is bent when the molded body is fired, and the resulting insulator 10 is bent. Here, the length L0 of the large diameter portion 11r2 of the shaft hole 11 of the insulator 10, the length L3 of the uneven portion 11ue on the inner surface of the shaft hole of the insulator 10, the parameter L3 / L0, and the bending of the insulator 10 The determination result is described. The bending test of the insulator 10 is performed by rotating the insulator 10 around the axis 0 while holding the front end side (lower side in FIG. 2) of the single insulator 10 so that the head at the rear end of the insulator 10 The measurement was performed by measuring the amount of shake. Here, the “head shake amount” is the maximum distance from the specified position on the head surface of the insulator 10 to the actual position. The “specified position of the head” is a position given by a design value of the distance from the axis O to the head surface.

  As the dimensions of the insulator 10, the test was performed by changing two dimensions, that is, the length L0 of the large-diameter portion 11r2 of the shaft hole 11 and the length L3 of the uneven portion 11ue. This is because, among the various dimensions described above, the bending of the insulator 10 affects only these two dimensions L0 and L3, and the other dimensions are considered to have little influence. That is, when the dimension L3 is increased with respect to the dimension L0, the ratio of the thin portion of the insulator 10 forming the large diameter portion 11r2 of the shaft hole 11 is increased. The end part is easy to bend. The other dimensions shown in FIG. 2 have little influence on the bending of the rear end portion of the insulator 10. In the first five samples S41 to S45, the length L0 of the large diameter portion 11r2 is set to 30 mm, and the length L3 of the uneven portion 11ue is changed. In the next five samples S51 to S55, the length L0 of the large diameter portion 11r2 is set to 40 mm, and the length L3 of the uneven portion 11ue is changed.

  According to the result of FIG. 5, it can be understood that the smaller the parameter L3 / L0, the better the bending of the insulator 10 is. The parameter L3 / L0 is preferably 0.6 or less, more preferably 0.5 or less, and most preferably 0.4 or less.

  The results of FIG. 5 are results when the uneven portion 11 ue to be fitted with the powder filling portion 60 is continuously provided in the female screw portion provided at the rear end of the shaft hole 11. That is, the length L3 of the uneven portion 11ue at this time is the sum of the length of the female screw portion for screwing with the terminal fitting 40 and the length of the uneven portion for fitting with the powder filling portion 60. However, as described above, the uneven portion for fitting with the powder filling portion 60 can be provided apart from the female screw portion for screwing with the terminal fitting 40. Also in this case, the total length L3 of the concavo-convex portions provided on the inner surface of the shaft hole of the insulator 10 (the length of the concavo-convex portions for fitting with the powder filling portion 60 + the female screw portion for screwing with the terminal fitting 40) If the length of the insulator 10 is excessively long, the bending of the rear end portion of the insulator 10 may be excessive. Therefore, also in this case, the length ratio L3 / L0 is preferably 0.6 or less, more preferably 0.5 or less, and most preferably 0.4 or less. However, depending on the type of the spark plug, the bending of the insulator 10 may not be a problem. In this case, the length ratio L3 / L0 may be set to a value exceeding 0.6.

Modification Examples The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the scope of the invention.

・ Modification 1:
As the spark plug, spark plugs having various configurations other than those shown in FIG. 1 can be applied to the present invention. In particular, various modifications can be made to the specific shapes of the terminal fitting and the insulator.

Modification 2
In the embodiment described above, the concavo-convex portion 11 ue to be fitted with the powder filling portion 60 is formed as a screw groove continuous with the female screw portion provided at the rear end of the shaft hole 11. It is possible to adopt various shapes and arrangements other than this. For example, the concavo-convex portion 11ue may have other concavo-convex shapes other than the screw grooves (for example, a plurality of island-shaped concave portions or convex portions, or a plurality of ring-shaped concave portions or convex portions arranged in the axial direction). However, the streak-like grooves parallel to the axis O are inferior to the other concavo-convex shapes from the viewpoint of enhancing the fixing force between the filling powder and the insulator 10. Therefore, it is desirable to adopt a concavo-convex shape other than the concavo-convex shape formed only by the streak-like grooves parallel to the axis O.

DESCRIPTION OF SYMBOLS 10 ... Insulator 10e ... Insulator tip 11 ... Insulator shaft hole 11stp ... Insulator shaft hole step 11r1 ... Insulator shaft hole small diameter part 11r2 ... Insulator shaft hole large diameter part 11ue ... Uneven portion on the inner surface of the shaft hole of the insulator (first uneven portion)
DESCRIPTION OF SYMBOLS 20 ... Center electrode 22 ... Front end side electrode part of center electrode 22a ... Unevenness processed part (2nd uneven part) of the front end side electrode part surface of center electrode
22e: the tip of the center electrode 24 ... the flange portion of the center electrode 26 ... the rear end side electrode portion of the center electrode 30 ... the ground electrode 40 ... the terminal fitting 50 ... the metal fitting 52 ... the tip of the metal fitting 54 ... the threaded portion 60 of the metal fitting 60 ... Powder filling part 62 ... 1st filling powder 72 ... 2nd filling powder 100 ... Spark plug

Claims (6)

An insulator having a shaft hole extending in the direction of the axis, a center electrode projecting from the tip of the shaft hole, a terminal fitting projecting from the rear end of the shaft hole, and a metal shell housing the insulator; The center electrode is provided on a distal end side electrode portion including a portion protruding from the distal end of the shaft hole of the insulator, and has a larger outer diameter than the distal end side electrode portion provided on the rear end side of the distal end side electrode portion. And a rear end side electrode portion which is provided on the rear end side of the flange portion and has an outer diameter smaller than that of the flange portion, and between the rear end side electrode portion and the inner peripheral surface of the insulator. In the spark plug filled with the first filling powder,
The spark plug is characterized in that an uneven portion is formed in at least a part of a portion of the inner peripheral surface of the insulator that is in contact with the filled first filling powder. The spark plug according to claim 1, wherein
The diameter of the shaft hole at the tip of the insulator is φd,
Of the concavo-convex portion, when the length in the axial direction of the portion in contact with the first filling powder is L1,
L1 / φd ² ≧ 0.3 mm ⁻¹
A spark plug characterized by satisfying. The spark plug according to claim 1 or 2,
The inner peripheral surface of the insulator has a stepped portion with which the inner diameter thereof increases toward the rear end side and the flange portion of the center electrode contacts at least a part of the inner surface.
In the axial direction, when the length from the rear end of the insulator to the stepped portion is L0, and the length of the uneven portion is L3,
L3 / L0 ≦ 0.6
A spark plug characterized by satisfying. In the spark plug according to any one of claims 1 to 3,
The spark plug is characterized in that the concavo-convex portion is formed by a thread groove continuous with a female screw portion provided at a rear end of the shaft hole so as to be screwed with a male screw portion of the terminal fitting. In the spark plug according to any one of claims 1 to 4,
A second filling powder is filled between the tip side electrode portion and the tip side inner peripheral surface of the insulator,
A spark plug, wherein a second uneven portion is provided on an outer peripheral surface of the tip electrode portion. The spark plug according to claim 5, wherein
The spark plug is characterized in that a length of the second concavo-convex portion in the axial direction is 10 mm or more.

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